In the United States, the Telecommunications Acts of 1992 and 1996 require that cable subscribers be given the option of owning the equipment required to receive cable services. To support competition in the market for so-called “host” devices (i.e. DTV receivers such as set-top boxes or integrated digital televisions), a Report and Order of the U.S. Federal Communications Commission (FCC) adopted on Sep. 10, 2003 and released on Oct. 9, 2003 entitled “Second Report and Order and Second Further Notice of Proposed Rulemaking” (referred to as the “Digital Cable Plug and Play Report and Order”), which is available at World Wide Web address hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-225A1.pdf and is hereby incorporated by reference hereinto, requires that cable operators make available security modules which are separable from host devices.
To satisfy the government's separable security requirements and to enable retail availability of host devices, point-of-deployment (POD) security modules have been developed. A POD security module (also known as a “POD module” or simply a “POD”) is a hardware device (with embedded firmware) provided by a cable provider which is intended to be plugged into a host device (or simply “HOST”) to facilitate the display of digital television programs that are otherwise protected by the cable provider's conditional access (CA) scrambling system. When a POD module is plugged into a host device designed to receive such a module, subscribers are able to view the secure digital video services and/or listen to audio services for which they have subscribed, which services may include premium subscription channels. POD modules are sometimes referred to by the trademark CableCARD™. Physically, a POD module may be a Personal Computer Memory Card International Association (PCMCIA) card or a smart card device, both of which are approximately the same size as a credit card (although PCMCIA cards are thicker than a credit card).
POD modules serve two functions. First, the POD module acts as a descrambler, allowing the cable provider to be assured that the host device at the subscriber premises is a secure device without which scrambled content will be unviewable. Second, the POD module acts as a translator between the possibly varying out-of-band (OOB) protocols used on different cable provider networks and a single protocol (described below) that is expected by the host device. In other words, by virtue of the POD translation, the host device is only required understand a single protocol, regardless of the OOB protocol(s) that may be operative on the cable provider network to which the host device is connected. Thus in the event of switching between cable providers or moving between different geographical areas, a subscriber should be able to continue using the same host device, provided that a new POD module is obtained from the new cable provider and plugged into to the host device. As well, this arrangement permits a cable provider to upgrade its network head-end without having to replace numerous set-top boxes at subscriber premises. The cable operator need only provide replacement POD modules in the event of an upgrade.
In a typical arrangement, a cable provider receives programming from various sources at its head-end and assigns it to channels. Each channel is a unique 6 megahertz (MHz) section of the cable provider's bandwidth which carries either a modulated digital signal that has been compressed or a modulated NTSC signal. At present, the standard most commonly used for compression is the MPEG-2 standard. MPEG-2 is a well-known multimedia compression and delivery standard developed by the Motion Picture Experts Group. The format of the MPEG-2 transport stream is in accordance with the ISO/IEC 13818-1 “MPEG-2 Systems” standard. The numerous 6 MHz channels are then transmitted over cables simultaneously to subscribers in the form of an analog radio frequency (RF) signal.
At the host device, an RF signal is received by a tuner within the host device. Depending upon the television channel selected by the subscriber (e.g. via a handheld remote control device), the tuner isolates one of the 6 MHz channels comprising the received signal and converts it to a fixed lower frequency. The output of the tuner is an analog signal representative of the tuned channel. This is referred to as a Forward Application Transport (FAT) channel.
The FAT channel is presented to a Quadrature Amplitude Modulation (QAM) demodulator within the host device. As is known in the art, a QAM demodulator converts the analog FAT channel to a baseband MPEG-2 transport stream, which is a stream of (digital) packets. A subset of the packets of this stream represent the program content that is to be viewed by the subscriber (with the remaining packets consisting of control packets, “metadata” packets containing information about the network, and possibly other program content, as will be described).
In order to prevent unauthorized viewing of subscription channels, programs transmitted by way of MPEG-2 transport streams are typically scrambled by the cable provider using a conditional access scrambling system. This is typically done for all but basic tier cable channels. The term “scrambling” is a legacy term which historically describes a technique developed in the 1970s whereby an analog cable television channel was reduced to a jumbled set of video images through removal of a synchronization signal or insertion of an interfering signal at the network head-end. In the digital MPEG-2 transport stream, it is more accurate to refer to a program as being “encrypted” rather than “scrambled”, since digital encryption techniques (not the above-described approach) are now employed to encrypt packets. However, the term “scrambled” is still commonly used to refer to this network head-end encryption, and the term “descramble” is still used to describe decryption of this encrypted program.
If a program comprising the MPEG-2 transport stream is scrambled, the MPEG-2 transport stream is forwarded to the POD module via the “HOST-POD interface.” The HOST-POD interface is an interface governed by a standard known as the ANSI/SCTE 28 2004 HOST-POD Interface Standard. This standard defines the physical interface, signal timing, link interface and application interface of the HOST-POD interconnection (i.e. the interconnection between the POD module and the host device). The ANSI/SCTE 28 2004 HOST-POD Interface Standard was developed by the American National Standards Institute and the Society of Cable Telecommunications Engineers. It is available at www.scte.org/documents/pdf/ANSISCTE282004.pdf, and is hereby incorporated by reference hereinto.
Assuming that a POD module is plugged into the host device, the MPEG-2 transport stream output by the QAM demodulator is received at the POD module. At the POD module, two steps are performed. First, the scrambled program within the MPEG-2 transport stream received from the host device is descrambled (i.e. decrypted). Second, the content is “copy protection” (CP+) re-encrypted and is provided back to the host device over the HOST-POD interface. The purpose of this re-encryption is to avoid unencrypted content from being transmitted, and possibly intercepted, between the POD module and the host device. Re-encryption may be performed using the Data Encryption Standard (DES). DES is defined in U.S. National Institute of Standards and Technology (NIST) Federal Information Processing Standards (FIPS) Publication 46-3 (Electronic Code Book mode of operation), which is hereby incorporated by reference hereinto. DES is a method of data encryption which uses a private (secret) key that must be known and used by both the sender and the receiver of the data. Packets representing minor channels that are not currently being viewed are passed from the POD module back to the host device unaltered.
At the host device, the CP+ encrypted MPEG-2 transport stream is received at a transport demultiplexer. Using the appropriate key, the transport stream is decrypted, and elementary audio and video streams of the tuned channel are extracted and forwarded to MPEG audio and video decoders for ultimate conversion to sound by speakers and display as moving images on a screen (respectively). In some cases, a IEEE 1394 data link device may transfer the compressed program to other devices (the number “1394” refers to the Institute of Electrical and Electronics Engineers (IEEE) 1394 standard, which is a well-known bus standard).
In the event that the program tuned in by the subscriber has not been scrambled by the cable provider, however, the HOST-POD interface is bypassed, and the MPEG-2 transport stream is instead transmitted directly from the QAM demodulator to the transport demultiplexer. In this case the transport demultiplexer need not perform any CP+ decryption on the transport stream. The bypassing of the HOST-POD interface is mandated by a Report and Order of the FCC entitled “Report and Order and Further Notice of Proposed Rulemaking” adopted and released on Nov. 4, 2003 (referred to as the “Broadcast-Protection Report and Order”), which is available at World Wide Web address hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-273A1.pdf. An objective of the Broadcast-Protection Report and Order is to prevent unscrambled content from being presented at an output of a host device.
In view of the MPEG-2 compression applied at the network head-end, which increases the amount of data that can be transmitted by way of a single 6 MHz analog channel as compared to traditional analog transmission, and in view of the various formats (as enumerated in Table 1 below) that are supported by digital television standards, each 6 MHz analog channel (referred to as a “major” channel) may actually consist of multiple “sub-channels” (referred to as “minor” channels). Each sub-channel may carry a different television program. The term “program” as used herein refers to a single stream of content including video, audio and related data. A program may of course include advertisements (i.e. commercials) in addition to scheduled shows.
TABLE 1DTV FormatsFormatCharacteristics480iThe picture is 704 × 480 pixels, sent at 60 interlaced framesper second (30 complete frames per second).480pThe picture is 704 × 480 pixels, sent at 60 complete framesper second.720pThe picture is 1280 × 720 pixels, sent at 60 complete framesper second.1080iThe picture is 1920 × 1080 pixels, sent at 60 interlaced framesper second (30 complete frames per second).1080pThe picture is 1920 × 1080 pixels, sent at 60 complete framesper second.
For clarity, the “p” and “i” in Table 1 are abbreviations for “progressive” and “interlaced” respectively. In a progressive format, the full frame updates up to every sixtieth of a second. In an interlaced format, half of the picture (i.e. a “field” comprising every other scan line of a display) is updated every sixtieth of a second. The 480p and 480i formats are known as standard definition (SD) formats, with 480i being roughly equivalent to a traditional analog TV picture. The 720p, 1080i and 1080p formats are referred to as high definition (HD) formats, otherwise known as “HDTV”.
Thus, a cable provider wishing transmit multiple programs over a single 6 MHz channel (known as “multicasting”) may for example transmit several SD minor channels over the major channel.
When a subscriber tunes into a scrambled (i.e. encrypted) minor channel within a major channel, the MPEG-2 transport stream representing the entire major channel—including all of the contained minor channels, even those which are not being viewed—is transmitted to the POD module via the HOST-POD interface. The POD module performs its descrambling and CP+encryption on only the minor channel of interest. If any of the other minor channels are not scrambled, those channels will be transmitted to the POD module in unscrambled form and back from the POD module in unscrambled form. This may disadvantageously permit an enterprising subscriber to access minor channels in an unencrypted form at the HOST-POD interface. Moreover, assuming that the unscrambled channels have been designated with a Redistribution Control (RC) descriptor indicating that the channels are not to be output at a digital output (e.g. a IEEE 1394, Ethernet or wireless output) without enabling protection technology associated with that digital output, such transmission of unscrambled content over the HOST-POD interface would also be in violation of the FCC's Broadcast-Protection Report and Order.
A solution which addresses at least some of the above noted disadvantages would be desirable.